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Rotary Joint with Torque Bias

IP.com Disclosure Number: IPCOM000049455D
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 52K

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Hendriks, F: AUTHOR


When a rotary hydraulic motor is externally loaded, unwelcome sudden motion can result on power down.

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Rotary Joint with Torque Bias

When a rotary hydraulic motor is externally loaded, unwelcome sudden motion can result on power down.

In rotary hydraulic actuators it is sometimes desirable to offset unbalanced torque on a joint. For instance, in Fig. 1, the weight W (this could be the hand) has a torque W sin 0 about the axis of a Motor M. Referring to Fig. 2, the idea proposed here is to fit the motor shaft with a permanent magnet which is free to rotate, on ball bearings, say, inside a non-circular cavity; an elliptical shape is shown here for purposes of discussion, but other shapes could be used also, depending on the desired moment angle relationship.

To obtain a large moment, the permanent magnet could be a samarium cobalt type. The housing is a high permeability ferro magnetic material (e.g., steel 1010). The varying moment in Fig. 2 results from the variation of reluctance with angular position. The non circular cavity can be fabricated with wire EDM (Electrical Discharge Machining) or N/C milling techniques.

As a corollary, the bias torque device and the motor can be combined as in Fig. 3. There, a revolute motor is shown with non magnetic stator and a rotor which is itself poled, or which is made such that it contains a high energy product permanent magnet. The rotor moves inside a circle cylindrical cavity as usual, but the material is non magnetic and the outside is now profiled to suit the desired moment versus angular displacement profile. As shown,...